The present invention relates to techniques for performing analog signal processing, and more particularly, to such techniques having dynamic power-scaling. Such techniques have particular applicability to portable communication applications.
In active filters; large dynamic range necessitates large power consumption. A common way to relax the dynamic range requirements is to use an automatic gain control (“AGC”) circuit in front of the filter. Every 3 dB increase in minimum signal level (Vmin) allows increasing the noise floor by 3 dB, which allows a decrease of power consumption and capacitor area by approximately a factor of 2. However, in most wireless receivers, the interferer power limits the allowable AGC gain for Vmin and makes high power consumption necessary in order to satisfy the signal to noise ratio (“SNR”) specification. As a result, the operation of portable application will be shorter due to the limited battery life.
A common solution to this problem is to distribute the AGC operation throughout the filter, further amplifying the signal as interferers are attenuated, which makes possible a reduction of the power consumption of the latter stages of filter. However, the power consumption of the first stages will still be high and constant. Generally, the first stages of a filter (or system) has the highest power consumption.
An alternative solution utilizing two selectable filters, each power-optimized for a different dynamic range, has been proposed in F. Behbahani, et. al., “Adaptive analog IF signal processor for a wide-band CMOS wireless receiver,” IEEE J Solid-State Circuits, vol. 36, pp. 1205-1217 (August 2001). However, this design has just two power-consumption settings, which may be unnecessarily limiting. Moreover, the output of the circuit unfortunately includes undesirable transients to switching.
Accordingly, there remains a need in the field for a technique for the dynamic power-optimization of analog active filters which permits multiple power level scaling and reduces undesirable transients.